Modern vehicles use wireless key fobs that restrict both interior access as well as the ability to operate the vehicle. Authorized vehicle users can carry the wireless key fobs and as they approach the vehicle it can determine whether the unique wireless signal transmitted by the key fob is authorized for access and/or operation. If so, the vehicle user can enter and subsequently start the vehicle. These systems are often referred to a passive entry passive start (PEPS) systems. Before the vehicle user can start the vehicle, it determines whether or not the key fob is located inside the vehicle. Given that the threshold for the determination of being inside of or outside of the vehicle can be relatively small, resolving the location of the key fob in the vehicle may call for a high degree of accuracy.
Presently, PEPS systems and key fobs use omni-directional antennas that receive wireless signals without regard to the direction from which they are received. These omni-directional antennas may be effective when used with active systems in which a user presses a button on a key fob to actively control a vehicle function, such as unlocking the doors. In those systems, the signal direction may not be important. But in PEPS systems, the wireless signal is used to determine the location of the key fob and omni-directional antennas can limit PEPS system performance. For example, the wireless signal transmitted by a key fob may reflect off of surfaces before ultimate receipt by an omni-directional antenna. When such reflections occur, determining the ultimate location of the key fob can be challenging. And these reflections occur more frequently as the frequency at which the key fob transmits increases.